Very Large Array Plus Pie Town Astrometry of 46 Radio Stars

We have used the Very Large Array (VLA), linked with the Pie Town Very LongBaseline Array antenna, to determine astrometric positions of 46 radio stars inthe International Celestial Reference Frame (ICRF). Positions were obtained inthe ICRF directly through phase referencing of the stars to nearby ICRF quasarswhose positions are accurate at the 0.25 mas level. Radio star positions areestimated to be accurate at the 10 mas level, with position errors approachinga few milli-arcseconds for some of the stars observed. Our measured positionswere combined with previous measurements taken from as early as 1978 to obtainproper motion estimates for all 46 stars with average uncertainties of ~1.7mas/yr. We compared our radio star positions and proper motions with theHipparcos Catalogue data, and find consistency in the reference frames producedby each data set on the 1-sigma level, with errors of ~2.7 mas per axis for thereference frame orientation angles at our mean epoch of 2003.78. No significantspin is found between our radio data frame and the Hipparcos CelestialReference Frame (HCRF) with largest rotation rates of +0.55 and -0.41 mas/yraround the x and z axes, respectively, with 1-sigma errors of 0.36 mas/yr.Thus, our results are consistent with a non-rotating Hipparcos frame withrespect to the ICRF.Comment: 29 pages, 8 figures, accepted for publication in the Astronomical Journa